1. Field of the Invention
The present invention relates to a vehicle automatic transmission, and more particularly to a control system of a vehicle automatic transmission having a multiple stage transmission gear mechanism connected with a torque converter.
2. Description of the Prior Art
Conventional vehicle automatic transmissions having a multiple stage transmission gear mechanism connected to a torque converter are adapted to automatically select one of the gear stages of the transmission gear mechanism in accordance with vehicle operating conditions so that start and shift operations can be obtained automatically. There is known an automatic transmission further including means for determining a vehicle drive property in accordance with a driver command in addition to the automatic shift control mode. An example of such an automatic transmission is shown in Japanese Patent Publication No. 48-210 for public opposition on Jan. 6, 1973. In this automatic transmission, there is provided a holding mode as a shift control mode wherein the transmission in is maintained at a predetermined gear stage irrespective of the driving condition of the vehicle when the driver selects the holding mode so that the vehicle can drive in accordance with the driver's commands.
In such an automatic transmission provided with a holding mode for the vehicle shift control in addition to the automatic shift control mode, a shift down operation is not made where the holding mode is selected even when the vehicle speed is reduced and an unloaded engine condition is produced. As a result, when an higher gear stage, such as the third stage of the D-range is selected, a restart operation is carried out under such higher gear stage after the idling condition has occurred so that a desirable acceleration speed cannot be obtained. Further, when the vehicle runs up hill, it is apt to reverse undesirably because of the lack of drive torque.